1. Field of the Invention
This invention relates to an in situ method of cleaning soil, particularly sand, and aqueous solutions such as water, that have been contaminated by, e.g., a spill of oil, chlorinated hydrocarbons, organic solvents, polychlorinated biphenyls (PCBs), and the like. The method relies on the formation of an aqueous slurry, the addition in separate steps of a detergent as well as a microorganism and an additive, and the regulation of temperature to reduce the presence of oil or other contaminants in the soil and/or water. The extraction of oil and/or other contaminants with the detergent may be repeated until their content is reduced to a point at which the soil and/or water are allowed to be degraded by indigenous microorganisms. This patent provides a method of cleaning contaminated soil and water, and an apparatus for so doing.
2. Description of the Background
Various methods have been employed in the past to remove contaminants from contaminated solids such as soil. U.S. Pat. No. 4,392,892 to Wagner et al discloses a method that impregnates soil, sand or residues that contain oil or petroleum hydrocarbons with an aqueous solution containing microbially-produced glycolipids. The resulting oil phase or emulsion leaves the capillaries of the oil-contaminating material, rises out of the aqueous phase, and is separated therefrom.
U.S. Pat. No. 4,424,081 to Giguere discloses a method for reconditioning soils contaminated with heavy crude, refined petroleum, and/or chemical products derived from similar sources. The method comprises mixing the soil with water, sodium hydroxide and steam to provide a blended slurry. The blended slurry is further agitated and heated in a sparger kiln to approximately 210.degree. F. (99.degree. C.) at the kiln outlet to provide a fine particle slurry. A caustic liquid is also injected at the kiln inlet to facilitate the extraction of the contaminants from the slurry. The separation of oil particles from the fine particle slurry is accomplished by first washing the slurry in a clarifier, followed by washing in flotation cell units, and subjecting the slurry to an aeration clarifier. A fatty acid or alcohol reagent is added at the aeration stage which produces a foam to which the oil particles adhere.
U.S. Pat. No. 4,574,013 to Peterson discloses a method for decontaminating soil containing halogenated contaminants by reaction schemes that are carried out in a slurry of soil and a non-aqueous reagent mixture. The non-aqueous reagent mixture of the Peterson patent contains an alkaline component and a sulfoxide catalyst. There are four possibilities suggested for the alkaline component: an alkali metal hydroxide, an alkali metal hydroxide/alcohol mixture, an alkali metal hydroxide/glycol mixture, and an alkoxide. The Peterson process employs a non-aqueous reagent mixture and, therefore, when wet soil is to be decontaminated, vacuum must first be applied to remove any water prior to contacting the soil with the non-aqueous reagent mixture.
U.S. Pat. No. 4,662,948 to Weitzman discloses a method for removing polychlorinated biphenyls (PCBs) and chlorinated dioxins from solids, particularly soil. The Weitzman method removes contaminants by contacting the solids with a non-aqueous liquid containing a halogenated hydrocarbon. A smaller amount of polar organic solvent, e.g., methanol, is preferably used. The polar organic solvent apparently improves the wettability of the contaminated solids and allows the halogenated hydrocarbon to more easily extract PCBs and dioxins.
A study published by the U.S. Department of Commerce (National Technical Information Service No. PB84-123637) funded by the United States Environmental Protection Agency and conducted by Rexnord, Inc. discusses requirements for mobile systems to extract spilled hazardous materials from excavated soils. The study lists the characteristics necessary for an effective extraction fluid. Chief among these characteristics is a solvent possessing low volatility at ambient conditions. A volatile solvent under ambient conditions, such as aqueous ammonia, is not considered a suitable extraction fluid by the above study to decontaminate soil.
Aqueous ammonia has previously been used as a solvent for cleaning mechanical devices. For example, U.S. Pat. No. 4,507,155 to Cheek discloses a cleaning composition that includes a chlorinated hydrocarbon liquid, a petroleum distillate, an aliphatic alcohol, and aqueous ammonia. The composition has two phases which must be shaken before application. The concentration of ammonia in the composition is kept low, e.g., 20-33% maximum, to prevent burns to the handler. The composition is disclosed as being suitable for removing dried printing ink from printing equipment such as printing rollers as well as for removing stains from textiles.
U.S. Pat. No. 4,906,302 to Bruya discloses a method for decontaminating solid materials by removing hazardous organic waste with aqueous ammonia. The resulting solution is then treated to recover the organic waste for disposal and the decontaminated soil is returned to the excavation site.
German OS No. 3,216,771 discloses a process for cleaning earth contaminated with toxic materials. In this process, the earth is, e.g., heated in a rotating drum and the resulting gas products are burnt.
German Patent Application No. P3,447,079 also refers to a process for the thermal treatment of contaminated earth. In this process the earth is treated at a temperature of at least 600.degree. C. and the resulting gas is also burnt. In the processes of the two German references described above, the gas contaminants are thermally removed from the earth at relatively high temperatures. This requires a relatively large amount of energy.
German OS No. 2,531,732 describes a process for the removal, treatment and regeneration of oil-contaminated soil. Oil and water-soluble noxious components are washed out in low surface tension water preferably a temperatures between 60.degree. and 90.degree. C. The material to be treated is comminuted and mixed with the cleaning medium in a spiral drum and then separated from the contaminant-binding cleaning medium by sedimentation in a clearing sump.
A similar process for the regeneration of soil, e.g., soil contaminated by oil, is shown in German OS No. 2,724,271. Contaminated soil is optionally comminuted, suspended in the form of a slurry in a liquid such as water, and then heated to a vaporizing temperature in a continuous flow chamber. The upper layer of the suspension is stripped off and separated in the chamber. The dissolved substances, however, are not washed out from the contaminated soil in such a process at the vaporization temperature of water.
U.S. Pat. No. 4,993,873 to Tippmer discloses a further method for extracting substances such as benzene, toluene, phenols and heterocyclic hydrocarbons from soil by suspending the soil in water and subjecting the thus formed slurry to a multi-stage water extraction at high temperature, and drying the extracted soil.
Accordingly, there is still a need of a simple and effective method and apparatus for cleaning oil-contaminated soil, particularly sand and water, that can be conducted at the site of an oil spill and provide a significant reduction in the oil content of the soil and the surface and subterranean water layers.